Mary-Kate and Ashley Olsen made a rare appearance at the Met Gala on Monday. The sisters, who usually step out for fashion's big night, hit the red carpet at the Metropolitan Museum of Art in NYC in coordinating ensembles. They then let loose and danced the night away together at Katy Perry's afterparty at the Boom Boom Room at the Standard Hotel. This also isn't the first time we've seen them in recent weeks. The sisters attended another (more relaxed) gala with Mary-Kate's husband, Olivier Sarkozy, in April.